ARTICLE Received 13 Sep 2011 | Accepted 10 Apr 2012 | Published 8 May 2012 DOI: 10.1038/ncomms1829 The Eutherian Armcx genes regulate mitochondrial trafficking in neurons and interact with Miro and Trak2 Guillermo López-Doménech1,*, Román Serrat1,*, Serena Mirra1, Salvatore D’Aniello2,†, Ildiko Somorjai2,†, Alba Abad3, Nathalia Vitureira1, Elena García-Arumí4, María Teresa Alonso5, Macarena Rodriguez-Prados5, Ferran Burgaya1, Antoni L. Andreu4, Javier García-Sancho5, Ramón Trullas3, Jordi Garcia-Fernàndez2 & Eduardo Soriano1 Brain function requires neuronal activity-dependent energy consumption. Neuronal energy supply is controlled by molecular mechanisms that regulate mitochondrial dynamics, including Kinesin motors and Mitofusins, Miro1-2 and Trak2 proteins. Here we show a new protein family that localizes to the mitochondria and controls mitochondrial dynamics. This family of proteins is encoded by an array of armadillo (Arm) repeat-containing genes located on the X chromosome. The Armcx cluster is unique to Eutherian mammals and evolved from a single ancestor gene (Armc10). We show that these genes are highly expressed in the developing and adult nervous system. Furthermore, we demonstrate that Armcx3 expression levels regulate mitochondrial dynamics and trafficking in neurons, and that Alex3 interacts with the Kinesin/Miro/Trak2 complex in a Ca2 + -dependent manner. Our data provide evidence of a new Eutherian-specific family of mitochondrial proteins that controls mitochondrial dynamics and indicate that this key process is differentially regulated in the brain of higher vertebrates. 1 Developmental Neurobiology and Regeneration Lab, IRB Barcelona;Parc Cientific de Barcelona, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED, ISCIII), Department of Cell Biology, University of Barcelona, Barcelona E-08028, Spain. 2 Department of Genetics, Faculty of Biology, and Institute of Biomedicine (IBUB), University of Barcelona, Barcelona E-08028, Spain. 3 Department of Neurobiology, Institut d′Investigacions Biomèdiques de Barcelona, CSIC, IDIBAPS, Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED, ISCIII), Barcelona E-08036, Spain. 4 Department de Patologia Neuromuscular i Mitocondrial, Hospital Universitari Vall d’Hebron Institut de Recerca (VHIR), Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), ISCIII, Barcelona 08035, Spain. 5 Department of Molecular and Cellular Physiology, Instituto de Biología y Genética Molecular (IBGM), Universidad de Valladolid & CISC, 47003 Valladolid, Spain. *These authors contributed equally to this study. †Present address: Department of Cellular and Developmental Biology, Stazione Zoologica Anton Dohrn, Villa Comunale 80121, Napoli, Italy (S.D); Centre for Organismal Studies, Im Neuenheimer Feld 230, University of Heidelberg, 69120 Heidelberg, Germany (I.S.). Correspondence and requests for materials should be addressed to E.S. (email: [email protected]). NatURE COMMUNicatiONS | 3:814 | DOI: 10.1038/ncomms1829 | www.nature.com/naturecommunications © 2012 Macmillan Publishers Limited. All rights reserved. ARTICLE NatURE COMMUNicatiONS | DOI: 10.1038/ncomms1829 itochondrial function is vital for neuronal viability, neu- signal peptide with a potential transmembrane domain), nuclear rotransmission and neural integration1–6. Synaptic neu- localization signals and putative mitochondrial targeting sequences Mrotransmission and integration events in nervous tissue (Fig. 1b), in agreement with our data indicating that Armcx genes take place at long distances from neuronal cell bodies (dendrites are targeted to. Taken together, these observations suggest that these and axons). Consequently, to ensure energy production in distal proteins have related physiological or cellular functions. Moreover, compartments, neurons orchestrate exquisite mechanisms that unusually, all Armcx-coding sequences are contained in a single regulate the transport and localization of mitochondria at active exon, whereas the Armc10 is a typical, multi-exon-containing gene synaptic sites7–11. Mitochondrial trafficking in neurons is mediated with the coding sequence split into at least eight exons. by Kinesin and Dynein motors and by several GTPases and adaptor On the basis of the above data, it is likely that the entire Armcx proteins, including Miro1/2, Trak2 or Mitofusins12–16. Mutations cluster originated in early Eutherian evolution by retrotransposition in genes encoding mitochondrial trafficking proteins often lead to of an Armc10 messenger RNA, and then by consecutive tandem neurological and neurodegenerative diseases17–19. duplication events in a rapidly evolving region of the Xq chromo- Members of the Alex protein family (Alex1–3; for arm-contain- some23, which also includes the Armcx-related G-protein-coupled ing protein lost in epithelial cancers linked to the X chromosome) receptor Gasp1–3 genes24. The precise time point for the genesis were initially described as putative tumor-suppressor genes, as their of the Armcx cluster, when key innovations of the mammalian expression is reduced in several epithelial-derived carcinomas, group took place, namely the origin of a well-developed placenta, including lung, prostate, colon and pancreas cancers20. While Alex1 or the increase in complexity of the central nervous system and and 2 are widely expressed, Alex3 is found mainly in the nervous the enlargement of the neocortex25, suggest that this cluster has system. Previously, we characterized Alex3 as a gene preferentially functions related to the above processes. Hence, the origin of the expressed in the upper layers of the developing cerebral cortex21. Armcx cluster may well have been linked to the enlargement of the A recent report described Alex3 as a Sox10-interacting protein neocortex, as marsupials are devoid of the Armcx cluster but have a that localizes in the mitochondria of OBL21 cells, and suggested a primitive placenta. novel signalling cascade between the mitochondria and the nucleus We next analysed the expression of Armcx genes during embry- through a Sox10/Alex3 protein complex22. Here, we describe the onic development and in the adult brain. At embryonic stages, evolutionary history of the Armcx cluster and provide evidence that Armc10 and Armcx3–6 genes were highly expressed in the devel- these genes encode a new family of proteins that regulates mito- oping neural tissues, neural crest derivatives and hind limbs, in chondrial dynamics and that is specific to Eutherian mammals. addition to other tissues that were specific for each gene (Supple- Furthermore, we show that Alex3 protein levels affect the dynam- mentary Fig. S5). We also found that Armc10 and Armcx1–6 genes ics and trafficking of mitochondria in neurons through interac- were widely expressed in the adult nervous tissue, especially in the tion with the Kinesin/Miro/Trak2 complex in a Ca2 + -dependent forebrain, including the cerebral cortex, hippocampus and thala- manner. We conclude that the Armcx/Arm10 genes encode a mus (Fig. 1c). We thus conclude that the Armcx genes encode for a new family of proteins that controls mitochondrial dynamics and Eutherian-specific set of proteins that is highly expressed in transport in neurons. neuronal tissue. Results Armcx and Armc10 genes encode for mitochondrial proteins. The Armcx cluster originated during the evolution of placentals. To study the subcellular localization of Armcx gene products, To gain insight into the function of Armcx genes, we surveyed the HEK293AD cells were transfected with complementary DNAs mouse and human genomes for similar sequences. Interestingly, a full (cDNAs) encoding full-length Armcx proteins fused to EGFP set of related genes map to the same region of the human (Xq22.1) or myc tags. In agreement with the protein domain predictions and mouse (X56/57cM) X chromosomes, with the sole exception of reported above, all the Alex proteins tested (Alex1, 2, 3 and 6) were the Armc10/SVH gene, which maps to the seventh human and the targeted mainly to mitochondria, which were visualized by cellu- fifth mouse chromosome23,24. This unusual organization prompted lar staining with MitoTracker (Fig. 1c; and Supplementary Fig. S6). us to analyse further the evolutionary genesis of this gene family Nuclear staining was also occasionally seen in individual cells. (Fig. 1a). Six homologues, named Armcx1–6 and a pseudogene (Fig. Transfection with a cDNA encoding Armc10 yielded an identical 1a), are arrayed in a single cluster in a portion of the X chromosome, pattern of mitochondrial staining (Fig. 1c). Many cells transfected which was proposed to be specific to placental mammals23,24. We with Armcx1, 2, 3 and 6 and Armc10 cDNAs showed an altered then surveyed all available vertebrate genomes and noted the absence mitochondrial network, in which mitochondria were aggregated of Armcx genes in non-Eutherian mammals, namely monotremes in the perinuclear region (Fig. 2a and Supplementary Fig. S6). We and marsupials, and in non-mammalian vertebrates, and its conclude that the Armc10/Armcx cluster encodes for a new fam- consistent presence in all Eutherian mammals, including the earliest ily of proteins targeted to mitochondria and possibly regulates the branching armadillo (Supplementary Figs S1–S3). Hence, the Armcx dynamics and distribution of these organelles. cluster originated at the beginning or early radiation of the most To gain insight into the functional role of Alex